When using telnet "invoke" method, if there is a [null] param, the response always be [null] 

dubbo> invoke com.alibaba.dubbo.demo.DemoService.sayHello(null)    // null as parameter
null

reason: 
InvokeTelnetHandler.isMatch(Class<?>[] types, List<Object> args)
    ...
    } else if (ReflectUtils.isPrimitive(arg.getClass())) {  // there should judge arg is null first

原因： InvokeTelnetHandler.isMatch(Class<?>[] types, List<Object> args)中判断arg的类型时未做null值判断, arg.getClass()抛出了空指针异常